Automatic shift transmissions with automatic double clutch transmissions are mostly provided with friction-synchronized gear clutches which can be activated, that is, engaged and disengaged respectively, through an actuatable gear setter and associated transmission elements, such as, for example, a shifting fork engaging with the respective gear setter on the one hand, and on the other hand through a shifting fork engaging in a gearshift sleeve of a shifting package including two gear clutches. In order to engage one gear, the associated gear setter is initially moved out of a neutral position to a synchronous position and the synchronization element of the gear clutch usually comprising two conical synchronizing rings is acted upon by a synchronizing adjustment force. In this way, a friction torque is generated in the synchronization element under the action of which the associated input shaft is accelerated or decelerated to the output side rotational speed of the gear clutch.
When synchronous running on the gear clutch is reached, the gear clutch can be engaged through a further displacement of the gear setter in the direction of the respective shifting position, owing to which the relevant gear is engaged by producing a positive-fit, non-rotational connection between a loose wheel of the relevant gear wheel set and the associated transmission shaft.
In order to guarantee rapid, comfortable, and low-wear engagement of the gears of an automatic step transmission, an exact as possible knowledge of the respective synchronization point is necessary. Furthermore, the accuracy of the method for determination of the operating parameters at which the synchronization element of a gear clutch is activated and the value of the engaged synchronous torque used to determine an operating parameter depends upon the exact knowledge of the synchronization point of the activated gear clutch.
A corresponding method is described, for example, in WO 2004/076 225 A1, in which initially the friction clutch of the load-free component transmission is partially engaged for adaptation of the clutch characteristics of a double clutch transmission. After reaching synchronous running on the friction clutch, the synchronization point of the gear clutch of a gear of the same component transmission is approached, and then the synchronization element of the gear clutch is acted upon with a rising adjustment force until the synchronous running is cancelled on the friction clutch. In order to ascertain the contact point of the friction clutch, the current value of the synchronous torque of the gear clutch is assigned to the clutch torque engaged on the friction clutch, so that the exact knowledge of the synchronous torque depending on the synchronization point determines the accuracy of the contact point obtained.
Accordingly, the synchronization point of a gear clutch or a gear setter is understood to mean the corresponding value of a relevant adjusting parameter of the gear setter or an associated transmission element, as for example the synchronization position of a gear shift bar or the synchronization pressure of a gear setter configured as a pressure setting cylinder, at which synchronization of the relevant gear clutch is approached and acted upon by an adjustment force for synchronization. Since the synchronization elements of gear clutches of an automatic step gear shift can be constructed differently and differ from one another due to finishing tolerances as well as different wear and tear even with identical construction, a gear-specific determination of the respective synchronization point is necessary.
In a known method for activation of an automatic gear shift according to DE 101 10 898 A1, the transmission parameters necessary for selecting and shifting are determined on a testing stand before installing the gear shift in a motor vehicle. In order to determine the synchronization position of the gear setter or the respective gear shift bar, it is provided that the input shaft is set in rotation, that a change in rotational speed of the input shaft is monitored, and that with activation of a gear setter in the direction of a shifting position, the attainment of the relevant synchronization position is determined on the basis of a rotational speed change of the output shaft lying above a predetermined threshold value.
A method for determination of a synchronization point in an automatic gearshift is known from DE 101 36 731 A1 in which an operating parameter that determines the adjustment force of the associated gear setter, such as, for example, the adjusting current of an electric motor, is obtained when the gear is engaged, and the relevant synchronization point is obtained on the basis of a significant rise of this operating parameter.
A method for shift optimization of an automatic transmission is proposed in DE 10 2004 017 794 B4, in which the second time derivative of the input shaft rotational speed is determined in connection with a shifting procedure during travel when engaging the target gear, and the synchronization point of the associated gear clutch is obtained on the basis of a significant change of this derivative of the input shaft rotational speed. Alternatively or additionally, the synchronization point of a gear clutch can also be obtained on the basis of a recorded change in the adjustment speed of the gear setter or the adjustment parameter of the gear setter, such as the adjusting current of an electric motor or the adjustment pressure of a pressure adjusting cylinder.